Viola - Plant or Not to Plant?

I've only been gardening for a short while, and every time I think I've got my head round something, another query crops up. I've been bought a tray of yellow violas that are already flowering; is it too soon to plant out, or are they hardy enough to go now?

Violas are as tough as old boots- mine have been outside all winter and they're flowering their socks off - they should be fine planted out now provided you're not actually knee deep in snow.

If they've been kept in shelter just introduce them to the colder weather gradually, putting them out by day and in a sheltered spot by night just for a few days - just so they're not too shocked by an English spring!

Thanks so much all! I can see this forum is going to become my life line - so sorry in advance for all the questions that will follow. I assume they have been inside a garden centre, so I'll try harding them off for a few days - maybe plant further into the week.

As soon as I acquire a viola I remove all flowers. I check root system.....don't know why but they often are very root bound....and tease out tight roots. I find they grow so much more quickly doing this and they flower better and for longer.
No.....I would not plant out yet. They were prob grown indoors so not hardened off. They are too small. I would remove all flowers and pot into small pots. Plant out in couple of weeks for a much better display